1. Field of the Invention
The invention relates to a driving technology for a switching element adapted to the case where overcurrent is detected in the switching element.
2. Description of the Related Art
A method of protecting a semiconductor switching element, such as an insulated gate bipolar transistor (IGBT) or the like, at the time of shortcircuit is known (see, e.g., “APPLICATION NOTES”, AN-984J (FIG. 5 on page 5), IR (International Rectifier) Corporation). According to the described protection method, if a malfunction, such as a load shortcircuit or the like, occurs, the gate drive voltage is rapidly lowered to a certain level, and then if after a period of time, the malfunction continues to exist, the gate drive voltage is shut off. This technology is intended to reduce the malfunction electric current and therefore extend the malfunction verification period.
However, in the related art described above, detection of overcurrent is followed by the rapid lowering of the gate voltage regardless of the on-state of the switching element. Therefore, the gate voltage is rapidly lowered even when overcurrent is detected during an early period in a turning-on process during which the gate voltage has not sufficiently risen. If the gate voltage is rapidly lowered when the gate voltage has not sufficiently risen, the switching element is rapidly turned off, so that the off-surge voltage increases.